The present invention relates to an improved system for in-situ drilling, and more particularly, to a system where the rate of drilling or other aspects of the drilling operation are regulated or controlled by monitoring one or more parameters, including a parameter of the fluid flow for disposing of the cuttings and dust.
Most earth drilling systems employ some form of rotary or percussion powered drills. Many advances in recent years have made the drilling operation more efficient to create better and faster drilling speeds, especially in rock layers. Typically, a drilling machine, such as for forming a hole for an explosive charge or for anchoring a roof bolt, includes a drill stem with a drill bit on the distal down hole section thereof. The stem/bit on a rotary drill machine is rotated by a spinner mounted on a drill head to form the drill hole. The rotary driving motion of the spinner is usually hydraulically or pneumatically generated and manually regulated by the operator of the drill machine.
Due in part to the advances in the technology, such as in regard to the drill bit and/or components of the drilling machine providing attendant easier and faster drilling, operators have become accustomed to set the controls to try to drill the hole in the least amount of time. In doing so, the spinner head is rotated and the feed of the drill head is engaged to move the drill stem into the hole as rapidly as possible. The operator typically changes these settings only in the event that a problem develops.
As a part of the more efficient drilling, the cuttings and dust must be collected and removed from adjacent the drill bit so that clean cutting edges are provided at the bottom of the hole to allow the most efficient contact with the rock, or other strata. Typically, a pneumatic or hydraulic cuttings/dust collection/suppression and removal system is employed. Pressurized air, or a suitable hydraulic fluid such as water, or an air/water mixture, is forced down a center passage through the drill stem to bail or pick up the cuttings and dust for disposal. It is also known to impose a vacuum on the center passage of the drill stem drawing air into the hole around the periphery of the drill stem, whereupon the cuttings and the dust particles are entrained and removed through the center passage. In either system, this withdrawn debris is pneumatically or hydraulically conveyed away from the drill hole. When using air, the cuttings and dust are then filtered out and disposed of in an appropriate manner. In systems where water is used, either exclusively or in a mixture with other fluids, an option is to simply allow the dust to be suppressed and then deposited outside the drill hole. In either case, airborne contamination is advantageously substantially eliminated.
A typical drilling arrangement and cuttings/dust collecting system is shown in U.S. Pat. No. 4,434,861 to Howeth. In this patent, the bailing air is supplied through the center passage of the drill stem and the cuttings/dust is removed from the hole by a vacuum head. Insofar as the ""861 disclosure is concerned, the advancement of the drill stem into the hole, and the rotation of the drill bit, are manually controlled by the operator. Other functions of the drilling system are however automatically controlled, such as the extending or retracting the drill stem with respect to the deck plate. In other words, the drill stem extends to the drilling position only when the drill stem is supplied with sufficient bailing air to be operative, and the drill stem is automatically retracted from the hole when the bailing air supply is terminated (see col. 14, lines 14-37).
Another feature of the Howeth patent is to provide an improved vacuum skirt around the hole and the drill stem so as to attempt to improve the sealing, and thus enhance the efficiency of the bailing operation by reducing the tendency of the bailing system to choke or overload. This patent also teaches the fundamental premise of making certain that the passageways are proportioned sufficiently larger than the drill hole to also help alleviate choking of the bailing air carrying the cuttings/dust (see column 14, lines 38-66). While this overall system is an improvement over prior art drilling machines, problems still arise with regard to choking or overloading the vacuum system, especially where the drill speed is increased beyond normal levels and when strata containing soft minerals, coal, shale, mud stone or the like debris are encountered in the drilling operation.
Other patents, such as U.S. Pat. No. 3,946,818 to Ek, disclose the efforts to improve the sealing of the skirt in a different manner for improving the flow so that choking does not occur as readily. Heretofore, approaches other than these stop gap methods to solve the same problem have simply not been successful, insofar as we are aware. In theory, the operator of the drilling machine is simply depended upon to try to anticipate any approaching choking or flow overload situation and then shut the machine down. Unfortunately, in an overwhelming percentage of times, this is not possible because of the response time factor, and the collecting system becomes overloaded. The entire drilling operation must then be shut down for an extended period, the drill stem and bit removed from the drill hole and all passageways cleared of the debris. Alternatively, drilling must be performed at a continuously reduced rate to compensate and thus prevent these intermittent overload conditions. This speed reduction obviously detracts from the efficiency of the overall drilling operation, especially in the usual case where the operator must drill several hundred boreholes per shift.
Other inventors have concentrated on improving other aspects of the drilling machines, such as with respect to an improved cyclone filter, as set forth in the England U.S. Pat. No. 5,320,188. Indeed, there have even been attempts to control the flow of pneumatic fluid to the drilling tool in an automatic fashion. In U.S. Pat. No. 4,936,397 to McDonald et al., the pneumatically controlled valve is operable to transmit an initial, extra strong pulse of air to initiate operation of the down hole drilling motor. Once the motor is operating, the valve is kept open at a lower pressure than is required to open it so that the drilling can continue at a lower energy level.
Similarly, energy saving is the impetus in U.S. Pat. No. 5,409,072 to Enlund et al., wherein the pneumatic air supply is provided by a compressor driven by a hydraulic drive motor with adjustable displacement. The pneumatic pressure supplied by the compressor is adjusted inversely proportional to the pressure primarily used to drive the percussion drill along its linear path, and/or the input pressure of the drive motor itself. In this manner, it is proposed that the energy required to operate the entire system is maintained substantially constant during all phases of the operation.
Thus, while many refinements have been made in drilling machines and their method of operation, there is a marked absence of more responsive control systems, and more particularly with regard to regulating the drill feed and driving in response to one or more parameters, such as the thrust acting on the bit or the pressure of the bailing fluid used in the cuttings/dust collecting or suppression system. Such concepts would have specific usefulness in improving the drilling efficiency especially for forming small (20-50 mm) diameter holes using rotary cutting tools and high tool feed forces. In such an arrangement, we have discovered that it would be especially advantageous to keep the drill penetration rate as rapid as possible, while at the same time controlling the rate of tool advance and/or rotation using feedback from the drill feed system and/or the cuttings/dust collection or suppression system. In this manner, clogging or overload and the deleterious side effects are avoided, while the service life of the bit is maximized. What we envision as a need in the underground mining industry, and particularly for drilling small diameter holes for installation of roof bolts, explosive charges or the like, is such an automatic control of not only the drilling operation, but also of various components associated therewith using a system that is simple in design and reliable in operation.
In accordance with a first aspect of the invention, an improved apparatus and method for controlling the operation of a drill stem and drill bit based on monitoring at least the status of the fluid flushing mechanism is provided. More specifically, the apparatus provides for substantially continuous in-situ drilling, collecting and disposing or suppression of the drill cuttings/dust by feedback of the level of negative or positive gauge pressure maintained in the flushing mechanism through a programmable controller. The control circuit is preferably a low power (4-20 ma) electronic circuit that is approved for all underground mines. Alternatively, a hydraulic or electro-hydraulic circuit providing a comparable function is contemplated. The inventive system is targeted primarily for forming small (20-50 mm) holes in virtually any type of mining operation, including soda ash, coal, trona, salt, potash, limestone, gypsum or the like.
In one embodiment for carrying out this principle, the apparatus comprises a drill stem having a drill bit, a feed device for feeding the stem/bit to form the drill hole, and a mechanism for flushing the cuttings/dust from the hole and conveying it to a remote location. A transducer tracks at least one parameter of the flow in order to provide a signal to the controller for regulating the rate of drilling so as to anticipate an approaching overflow condition. By utilizing such a system, the cuttings/dust and other debris are efficiently removed to eliminate or minimize airborne contamination. This objective is accomplished in a controlled manner without ever reaching an overload condition in the flushing mechanism that could lead to clogging and deleterious downtime.
The parameter may be sensed through the transducer coupled to a transfer duct of the flushing mechanism. The feedback arrangement provides for a corresponding signal to be generated by the transducer indicative of the pressure in the duct. In return, the controller is operative to regulate the operation of the feed device for the drill head to vary the rate of feed dependent on the signal level. In addition, the drive unit for rotating the drill stem/bit can be controlled in concert with the feed.
Given the objective requirement for simplicity, the flushing mechanism includes for vacuum generation a standard blower connected to the transfer duct through a filtering system assembly, including a standard filter. The filter may comprise tortuous path, cylinder cartridges and/or cyclone filters, and as outlined in detail below, the system may include a pre-cleaner for removing larger particles from the bailing fluid flow and prevent them from reaching the filter. The filter is typically designed to capture relatively small or fine particles only, and is subject to overloading if the pre-cleaner is not regularly emptied. Hence, the pre-cleaner must be periodically emptied/cleaned to dispose of the larger particles of the cuttings, as well as any smaller dust particles. Using the control of the present invention, the pre-cleaner may also be caused to automatically empty, such as based on reaching a particular point in the drilling cycle.
The controller can be used to program and adjust the threshold level of the pressure corresponding to the approaching overload so that maximum drilling efficiency is obtained for any particular type of mining, or related operation, being performed. The window of operation is set to ensure substantially continuous drilling and eliminate false signals of approaching overload. The upper and lower thresholds of the gauge pressure in the flushing mechanism can be varied to establish the optimum rate of feed and/or drilling rotation.
In a second embodiment, the flushing mechanism utilizes pressurized fluids, such as water. The fluid is pumped through the center passage of the stem/bit. A slurry of cuttings/dust is formed and forced out of the drill hole for easy disposal, while simultaneously suppressing the dust to eliminate airborne contamination. Any increase in positive gauge pressure is sensed through the transducer in the transfer duct to anticipate any approaching overload condition. As in the preferred embodiment, corrective adjustment is automatically made in the drilling rate.
With respect to the related method, the in-situ drilling and collecting or suppressing of the drill cuttings and dust from the drill hole includes drilling the hole with a drill stem and bit, flushing the cuttings/dust from the drill hole, monitoring at least one parameter of the flow of the bailing fluid, and regulating the rate of drilling to control the parameter during both a normal and approaching overflow condition. By use of this method, the drilling operation can be continuous as the collection or suppression of cuttings and dust from the drill hole is carried out in a controlled manner.
In accordance one version of the method, the parameter being monitored is the vacuum or negative fluid pressure level in the flushing mechanism. The regulating step is preferably concerned with the rate of feed of the drill stem into the drill hole. That is, the feed rate, including from zero to maximum, is made dependent on at least the signal level of the negative gauge pressure sensed in the transfer duct during the step of collecting and conveying the cuttings/dust or otherwise suppressing the dust. As an additional feature, the use of a programmable controller, or an equivalent adjustable operating hydraulic or electro-hydraulic valve, allows the addition of the step of adjusting the threshold of the approaching overload of the flushing mechanism for maximum efficiency. Also, adjustment of the reset window of the gauge pressure is contemplated. Close control of the threshold and the reset window helps in establishing the optimum rate of feed for the drill stem and thus the drilling efficiency.
In more specific terms, in the case of vacuum flushing, the adjusting step is performed by setting the threshold level of the vacuum/negative gauge pressure in the range of 10% to 20% above the normal negative pressure level, and to reset to normal vacuum within 0.5-4 inches Hg. as the threat of the overload is passed. If desired, the regulating step can include changing the speed of the rotary driving of the drill stem, also depending on the signal level from the transducer and coordinated with the linear feed rate of the drill stem.
Thus, under optimum operating conditions, the regulating step can perform so as to maintain the parameter in the flushing mechanism, such as the vacuum level or rate of flow of the fluid, so as to be substantially constant. Also, while the regulating step, as controlled by the programmable controller, can be made to vary the drill head feed and the spinner rotation, the preferred embodiment at present is to actually stop the feed of the drill stem and/or the spinner during an approaching overload condition, and to automatically restart the feed/rotation at the optimum rate when the potential or threatened overload condition is past.
A related aspect of the invention is to also automatically control other aspects of the drilling operation. For instance, the emptying of a component of the filtration system, or the opening and closing of structures, such as the clamp on the drill guide, may be effected at a particular point in the drilling operation, such as in response to the position of the drill stem/bit. Such automatic control eliminates the need for constant operation intervention, and may reduce the chance of errors. Using a manul input device, such as a joystick, to switch from automatic to manual control is also possible to allow the operator to take over in the event a problem arises.
In accordance with yet another aspect of the invention, a method and apparatus for controlling the drilling automatically based not only on a parameter of the bailing fluid flow, but also on a sensed parameter relating to the thrust experienced by the drill bit or stem is disclosed. In one embodiment, the apparatus comprises a feed device for feeding the drill stem and bit to form the drill hole at a feed rate corresponding to a first flow of a driving fluid under pressure. A sensor monitors a first parameter relating to the thrust acting on the drill stem and bit, such as by monitoring the feed pressure of the first flow of the driving fluid, and generates a first signal. Additionally, a flushing mechanism is provided for flushing cuttings and dust from the hole by bailing fluid flow. A transducer monitors a second parameter of the bailing fluid flow, such as the negative or positive gauge pressure, to the loading of the flushing mechanism and generates a second signal. A controller is responsive to the levels of the first and second signals for substantially automatically and continuously regulating at least the feed rate depending on one of the thrust acting on the drill bit or the loading of the flushing mechanism. As a result of regulating the feed rate based on both thrust and the operation of the flushing mechanism, not only is the consumption of the bit reduced, but the overall drilling operation is also optimized by preventing overloading.
In one embodiment, the controller controls a first directional value to regulate the first flow to maintain an optimum feed rate corresponding to a particular level of thrust. Preferably, the first valve is initially adjusted by the controller to maintain the flow such that the drill bit is fed at a preselected feed rate for the bit, which may be chosen according to the particular strata being drilled. Then, the position of the first valve is selectively adjusted by the controller during feeding in accordance with the level of the first signal, which is preferably a sensed feed pressure, to regulate the first flow until an optimum feed rate corresponding to the optimum level of thrust experienced by the drill bit. To prevent overloading, the controller maintains the optimum feed rate to keep the thrust at or below a predetermined target thrust. The target thrust is below a maximum predetermined level that may result in excessive wear on the bit or bending of the drill stem. The target level of thrust may be selected by the operator based on the particular bit and the drilling conditions.
Preferably, the first valve is adjusted by the controller to regulate the first flow to maintain the feed rate at a certain level or decrease it a predetermined amount when a substantial decrease in the feed pressure signal is detected by the controller, such as in response to the drill bit encountering a void in the earth. The amount of the substantial decrease in the feed pressure required to cause the controller to reduce the feed rate and the predetermined amount of the reduction are both selectively adjustable, such as by the drill operator during set-up, based on the particular drill bit or drilling conditions. The controller may also adjust the position of the first valve to reduce the flow of the driving fluid and hence the feed rate a predetermined amount when the feed pressure falls below a predetermined level indicative of a low thrust condition, such as when the drill bit encounters a strata in the earth substantially comprised of a soft material.
A drive unit for driving the drill bit at an initial rotational speed may also be provided. The rotational speed is regulated by the controller by adjusting the position of a second directional valve through which a second flow of a driving fluid under pressure passes to the drive unit. The controller may continuously regulate the position of the second valve to maintain the rotational speed at an optimum level based on the feed rate. Preferably, the controller prevents the second valve from closing beyond a certain point to maintain the rotational speed at or above a minimum level, or from opening beyond a certain point such that the rotational speed exceeds a maximum level, regardless of the feed rate dictated based on the sensed parameters.
The controller may also be programmed to include a first threshold level of the gauge pressure of the bailing fluid flow. Depending on the level of the gauge pressure relative to this threshold level, the controller may also adjust the first valve regulating the first flow of fluid to the feed device to regulate the feed rate. In particular, in the case where this first threshold level is exceeded, the controller either maintains the valve at the current position or adjusts the first valve to decrease the feed rate when the signal level reaches the first threshold level. In addition, the controller may operate to: (1) prevent the first valve from opening to increase the feed rate from the optimum level if the gauge pressure remains within a predetermined range above the first threshold level and signal a burst of rotary speed; (2) close the first valve to reduce the feed rate from the optimum level if the signal level of the gauge pressure exceeds a predetermined range above the first threshold level and signal a burst of rotary speed; and (3) close the first valve to stop the feeding of the drill bit and signal the feed unit to back the drill bit out of the hole a predetermined distance when a second threshold level of the gauge pressure that exceeds the predetermined range is reached. In the latter case, the controller may also open the first valve to resume the feeding of the drill bit once the signal level drops below the first threshold level.
A related aspect of the invention is to provide a method for automatically controlling the feeding of a drill stem and bit into the earth for forming a drill hole. The method comprises feeding the drill stem and bit into the earth at a feed rate; flushing the cuttings and dust from the drill hole by bailing fluid flow; continuously monitoring a first parameter relating to a thrust acting on the drill bit during feeding and a second parameter relating to the bailing fluid flow; and automatically and continuously regulating at least the feed rate based on one, and preferably both of the first and second parameters. As a result, the cuttings and dust are flushed in a controlled manner to substantially eliminate airborne contamination in a continuous and optimum drilling operation, while consumption of the bit is simultaneously optimized by controlling the feed rate based on thrust.
In one embodiment, the feed rate is initially set at a predetermined feed rate for the drill bit selected for a particular job, based on the drilling conditions. From this level, the feed rate is continuously regulated, which maintains the feed horsepower at a substantially constant level. In addition to optimizing energy use, controlling the feeding in accordance with the thrust reduces wear on the bit and extends its service life. Preferably, a predetermined target level of thrust is stored that is less than a level that may result in damage to the bit or stem, and the regulating step includes preventing the first parameter from exceeding this target level of thrust, such as by regulating the feed rate. This xe2x80x9cclippingxe2x80x9d addresses any lag in the response time required to make an adjustment in the feed rate to avoid reaching excessive thrust levels, and thus reduces the potential for a catastrophic failure.
The method may further include the step of maintaining the feed rate at a predetermined level or reducing the feed rate a predetermined amount when a substantial decrease in the first parameter corresponding to the thrust occurs, such as in response to the drill bit encountering a void in the earth. The amount of the substantial decrease in the first parameter relating to thrust required to trigger the reducing of the feed rate is preferably selectively adjustable, such as by the drill operator, to avoid nuisance trips. The amount of the reduction in the feed rate, or the predetermined level, may also be selectively adjusted. In addition to this void detection feature, the method may include reducing the feed rate a predetermined amount or setting it at a predetermined level when the first parameter falls below a predetermined value corresponding to a low thrust condition. This low thrust condition may result when the drill bit encounters a strata in the earth substantially comprised of a soft material.
Preferably, the step of feeding further includes simultaneously rotating the drill bit at a rotational speed that is dependent on the feed rate. In this case, the regulating step may include preventing the rotational speed of the drill bit from dropping below a predetermined minimum level or exceeding a maximum level regardless of the feed rate. Advantageously, this prevents excessive rotational speeds from being reached at the upper end and stalling at the lower end, including even when the feed rate is adjusted to relatively low levels corresponding to high thrust conditions.
It is also preferable to perform the flushing by vacuum, in which case the second parameter being monitored is a negative gauge pressure of the bailing fluid flow. Thus, in addition to controlling the feed rate based on the thrust and the rotary speed based on the feed rate, the method may further include the steps of: (1) setting a first threshold level of the negative gauge pressure and maintaining the feed rate at a current level or decreasing the feed rate when the gauge pressure reaches the first threshold level, (2) preventing any increase in the feed rate if the signal level of the negative gauge pressure levels off, such as by remaining within a predetermined range above the first threshold level; and (3) reducing the feed rate if the signal level of the negative gauge pressure exceeds a predetermined range above the first threshold level. These steps further enhance the drilling operation by preventing deleterious clogging resulting from an overload of the flushing mechanism. Signaling a burst in the rotary speed upon reaching the first threshold level is also desirable for this purpose.
Stopping the feeding of the drill bit and backing it out of the drill hole a predetermined distance may also be effected when a second, threshold level of the negative gauge pressure exceeding the predetermined range is reached. This serves to prevent a failure in the event of excessive clogging, such as when a strata comprised of clay or the like is encountered. Feeding is resumed at the optimum rate once the signal level corresponding to the gauge pressure of the bailing fluid flow drops below the first threshold level.